The invention relates to an optical disk drive and, in particular, to a circuit for writing a given format of modulation signal onto an optical disk and reproducing the modulation signal therefrom.
Due to widened use of compact disks recently, the optical disk drive, i.e., the optical writing and reproducing system has enlarged its application area to a video system or an auxiliary memory in a computer, as well as an audio system. This trend is mostly caused by some excellent advantages of the optical disk drive that it is capable of writing information onto the optical disk and read out the information from the disk even without making any physical contact with the surface of the disk, and of storing onto a single optical disk a large amount of information up to more than several hundreds of Mega-bytes to Giga-bytes, as compared to traditional data media such as a magnetic audio or video tape, or any other data storage system.
One known rewritable compact disk drive system is shown in a block diagram of FIG. 1, and part of various output waveforms therein are shown in FIGS. 2A to 2F, wherein FIG. 2A is a system clock. In write sequence, digital data from A/D converter 61 is made into an 8-bit signal with an error correction bit in an error correction circuit 62, which is applied to an eight-to-fourteen modulation (hereinafter referred to as EFM) circuit 63. Then, the 14-bit EFM signal of FIG. 2B is applied to a write pulse generator 64 from which output is sequentially written on the optical disk 68 through to a laser power controller 65 and a pickup 66. In the meantime, in read sequence the pickup reads out the written signal from the disk to convert the signal into an electrical signal and then deliver the signal into a pre-amplifier 69 for amplifying to an adequate level. The amplified analog signal is then applied into a slicing and reshaping circuit 72, a tracking circuit 70 and a focusing circuit 71. The analog signal of the pre-amplifier is digitized in the slicing and reshaping circuit and is then applied to an EFM demodulation circuit 73 to obtain a demodulated EFM signal, which is inputted to a D/A converter 75 through an error correction circuit 74.
In this optical reproducing system however, a number of the write pulse must be changed depending upon a duty period of logic high level of the EFM signal to be written onto the disk during the write operation. Moreover, the high period of the write pulse should be reduced as the number of the write pulse increases, so that there would be made no influence from any adjacent write pulses. Thus, such a limitation inevitably leads to a complicated circuit construction in the known optical disk drive system.